Method for manufacturing a semiconductor device utilizing an anodic oxidation

Abstract

An anodic oxide containing impurities at a low concentration and thereby improved in film quality, and a process for fabricating the same. The process comprises increasing the current between a metallic thin film and a cathode until a voltage therebetween reaches a predetermined value, and maintaining the voltage at the predetermined value thereafter.

What is claimed is: 
     
       1. A method of manufacturing a semiconductor device comprising the steps of: forming a gate electrode on an insulating surface;   applying a voltage between said gate electrode and a cathode through an electrolyte therebetween, with said gate electrode used as an anode;   increasing monotonically a current applied between the gate electrode and the cathode until the voltage therebetween reaches a first value;   then, maintaining said voltage at said first value for a first duration, thereby forming an anodic oxide film on said gate electrode;   forming a channel forming semiconductor layer over said gate electrode with at least said anodic oxide film therebetween.   
     
     
       2. The method of claim 1 wherein said current is increased in a stepwise manner. 
     
     
       3. The method of claim 2 wherein said current is increased at a constant rate. 
     
     
       4. A method of manufacturing a semiconductor device comprising the steps of: forming a semiconductor thin film;   forming an insulating film including at least a gate insulating film on said semiconductor film;   forming a gate electrode on said insulating film, said gate electrode comprising an anodizable material;   applying a voltage between said gate electrode and a cathode through an electrolyte therebetween, with said gate electrode used as an anode;   increasing monotonically a current applied between the gate electrode and the cathode until the voltage therebetween reaches a first value; and then   maintaining said voltage at said first value for a first duration.   
     
     
       5. The method of claim 4 wherein said current is increased in a stepwise manner. 
     
     
       6. The method of claim 4 wherein said current is increased at a constant rate. 
     
     
       7. A method according to claim 4 wherein said gate electrode comprises a material selected from the group consisting of aluminum, tantalum titanium and silicon. 
     
     
       8. A method of manufacturing a semiconductor device having at least source, drain and channel regions, and a gate electrode adjacent to the channel region, said method comprising the steps of: forming the gate electrode on an insulating film, said gate electrode comprising an anodizable material;   applying a voltage between said gate electrode and a cathode through an electrolyte therebetween, with said gate electrode used as an anode;   increasing monotonically a current applied between the gate electrode and the cathode until the voltage therebetween reaches a first value; and then   maintaining said voltage at said first value for a first duration.   
     
     
       9. A method of manufacturing a semiconductor device having at least source, drain and channel regions, and a gate electrode adjacent to the channel region, said method comprising the steps of: forming the gate electrode on an insulating film, said gate electrode comprising an anodizable material;   applying a voltage between said gate electrode and a cathode in an electrolyte, with the gate electrode used as an anode;   anodizing the surface of said gate electrode by increasing the voltage between the gate electrode and the cathode until the voltage reaches a first magnitude while keeping an applied current at a first constant value; and then   increasing the voltage between the gate electrode and the cathode subsequently after the voltage reaches the first magnitude while keeping the applied current at a second constant value, said first value being different from said second value,   wherein an increasing rate of said voltage is increased during said anodization.   
     
     
       10. A method according to claim 9 wherein said gate electrode is located over the channel region. 
     
     
       11. A method according to claim 9 wherein said gate electrode is located below the channel region.